Multi-segmented or multi-linked hydraulically-actuated manipulators such as excavators, until recently, have been controlled by the operator controlling each individual link, (i.e. each actuator for each link) by individually adjusting the flow of hydraulic fluid to an actuator for a selected link or arm segment to obtain a desired movement of the selected link. The operator had to coordinate the necessary motions for each of the links or segments of the arm to obtain the desired movement of the end point of the arm.
To simplify the operator's work resolved or coordinated motion control systems have been incorporated into said multi-linked hydraulic arms. These control systems generally employ a computer using inverse kinematics to determine the necessary angular adjustment of each link to obtain the desired end point movement and to control the hydraulic systems, i.e. the servo valves which in turn control the main hydraulic valves to obtain the flow of fluid required to the actuator for each segment of the arm to obtain the desired end point motion. One such system has been described in EPC Publication No. 0,330,383 published Aug. 30, 1989.
As these systems became more sophisticated it became apparent that further elaborations would be helpful to ensure smoother operation and to ensure the actual arm movements and desired arm movements as requested by the operator do not become too far apart. A system for so controlling the flow to the various actuators to maintain a desired relationship between the actual position and the desired position of the arm segments is disclosed in U.S. patent application Ser. No. 07/556,417 filed Jul. 24, 1990 Frenette et al. In this system the desired movement or position is compared with the actual movement or position of the arm and the signals for valve adjustments are modified in accordance with the difference between the actual position and desired position to ensure that the desired position as seen by the control remains reasonably close to the actual position. This type of system will accommodate slow movement of the boom or the like when the capacity of the equipment is not sufficient to meet the demands placed on it by the manual controller.
As taught in an application by Sepehri et al filed on even date herewith, the load on the actuator being manipulated, i.e. on the particular arm segment being moved by a specific actuator, influences the flow necessary to obtain the desired movement of the arm segment. To compensate for this variation in flow a control system is provided wherein the hydraulic pressure on opposite sides of a piston of an actuator for a given link or arm segment are measured and these pressures are considered in the control algorithm for setting the spool position in the valve controlling flow to or from that particular actuator.
The disclosures of the above applications are incorporated herein by reference.